Study of microstructure effects on the photo-induced Metal-insulator transition in VO$_2$ thin films grown on Al$_2$O$_3$ and TiO$_2$*

We studied the optical response of the VO$_2$ thin films undergoing photo-induced metal-insulator transition (MIT) of VO$_2$ and found the change in reflectivity over time to be highly dependent on the substrate on which the film was grown [1]. Specifically, we have looked at two different VO$_2$ thin film samples, one grown on TiO$_2$ and one grown on Al$_2$O$_3$, in a pump-probe configuration, and found that the strain and differences in microstructure resulted in substantial difference in the fluence threshold needed to induce MIT, as well in the relaxation times back to the insulating state. By mounting the films in a cryostat, we also found that the fluence needed to achieve full MIT for the film on TiO$_2$ substrate did not depend on the sample temperature, implying that different mechanisms may be playing a stronger role in one film rather than the other for an optically induced transition. \\[4pt] [1] E. Radue et al. arXiv:1410.6438 (2014)